Micro-electro-mechanical-system (MEMS) resonator and manufacturing method thereof

ABSTRACT

A micro-electro-mechanical-system resonator, includes: a substrate; a fixed electrode formed on the substrate; and a movable electrode, arranged facing the fixed electrode and driven by an electrostatic attracting force or an electrostatic repulsion force that acts on a gap between the fixed electrode and the movable electrode. An internal surface of a support beam of the movable electrode facing the fixed electrode has an inclined surface.

This is a continuation of application Ser. No. 11/561,146 filed Nov. 17,2006. The disclosure of the prior application is hereby incorporated byreference in its entirety.

BACKGROUND

1. Technical Field

The present invention relates to a MEMS resonator and a manufacturingmethod thereof.

2. Related Art

In recent years, MEMSs have exhibited a favorable growth in the usagethereof for apparatuses such as acceleration sensors and video devices.MEMS is an acronym of Micro-Electro-Mechanical System, and there arevarious interpretations for what encompassed within the conceptual rangethereof. Generally, it means, “fine functional devices produced usingsemiconductor manufacturing techniques”, while in some cases, it is alsoreferred to as “micro machine”, or “micro system technology (MST)”.Those devices are manufactured based on fine processing techniquesdeveloped for fabrication of semiconductors. Currently, MEMSs aremanufactured individually, or, produced onto the integrated circuit (IC)in a process after the manufacturing thereof.

Along with the trend of semiconductor devices becoming smaller and areformed in higher integration, through holes or contacts holes(hereinafter simply referred to as “holes”) are made finer; hence a highreliability is required in metallization. Therefore, those holes requirea higher coverage ratio of wiring metal. A semiconductor devicemanufacturing method has been suggested which improves the coverageratio of the wiring metal, in the case where the aspect ratio of holessuch as through holes or contact holes is large. The method includes: aprocess for forming in advance a stopper film in a vicinity of thebottom of a hole to be formed, in a location surrounding the hole; and aprocess for forming a sidewall on the internal wall of the stopper film.JP-A-5-6891 is an example of related art.

Moreover, in a method for manufacturing a semiconductor device such asan insulation gate type device having a thick field oxide film, if theprocessed shape of the field oxide film is deficient, wire thinningoccurs in the gate electrode or in the main wire through which a maincurrent flows at a tapered edge of the field oxide film, the wire beingcomposed of Al and the like. In an extreme case, a step disconnection ofwire occurs, significantly impairing the reliability of electrodewirings. In order to reduce the occurrences of such problem, asemiconductor manufacturing method is suggested, in which a taper at anarbitrary angle meeting the thick field oxide film is easily formed anda control over the taper angle processing is improved. JP-A-7-66280 isan example of related art.

Sidewall-shaped etching residue in a MEMS structure of a MEMS resonatorhas been either removed by slightly strong over etching, or, left as itis. In the coming years, it will be necessary to flatten the MEMSstructure in a MEMS process performed simultaneously with an ICmanufacturing. Therefore, if the occurrence of the sidewall-shapedetching residue in the MEMS structure can be prevented, the reliabilityof the MEMS resonator can be increased.

SUMMARY

An advantage of the present invention is to provide a highly reliableMEMS resonator and a method for manufacturing the same, by preventingthe occurrence of the sidewall-shaped etching residue in the MEMSstructure.

According to a first aspect of the invention, a MEMS resonator includes:a substrate; a fixed electrode formed on the substrate; and a movableelectrode, arranged facing the fixed electrode and driven by anelectrostatic attracting force or an electrostatic repulsion force thatacts on a gap between the fixed electrode and the movable electrode;wherein an internal surface of a support beam of the movable electrodefacing the fixed electrode has an inclined surface.

According to the above first aspect of the invention, since the internalsurface of the support beam of the movable electrode is inclined, it ispossible to make the cross-sectional shape of the support beam of themovable electrode to be smooth, thereby preventing the occurrence of asidewall-shaped etching residue. Hence, the status of disturbance tomovability of the MEMS structure or a current leak is improved, therebyproviding a highly reliable MEMS resonator.

In this MEMS resonator, the inclined surface may have an inclinationangle.

According to a second aspect of the invention, a MEMS resonatorincludes: a substrate; a fixed electrode formed on the substrate; and amovable electrode, arranged facing the fixed electrode and driven by anelectrostatic attracting force or an electrostatic repulsion force thatacts on a gap between the fixed electrode and the movable electrode;wherein the fixed electrode has a tapered surface on a side thereof.

According to the above second aspect of the invention, the taperedsurface of the side of the fixed electrode makes theside-cross-sectional shape of the fixed electrode smooth, therebypreventing the occurrence of a sidewall-shaped etching residue. Hence,the status of disturbance to movability of the MEMS structure or of acurrent leak is improved, thereby providing a highly reliable MEMSresonator.

In this MEMS resonator, the tapered surface may have an inclinationangle.

In this MEMS resonator, the gap may have a constant distance.

According to a third aspect of the invention, a method for manufacturinga MEMS resonator includes: forming, on a substrate, a fixed electrodehaving a sidewall on a side thereof; and forming a movable electrodeabove the fixed electrode, having a gap in between, and arranged to facethe fixed electrode.

According to the above third aspect of the invention, by forming thesidewall on the side of the fixed electrode, the internal surface of thesupport beam of the movable electrode is inclined; hence it is possibleto make the cross-sectional shape of the support beam of the movableelectrode to be smooth, thereby preventing the occurrence of asidewall-shaped etching residue. Consequently, the status of disturbanceto movability of the MEMS structure or of a current leak is improved,thereby providing the method for manufacturing a highly reliable MEMSresonator.

According to a forth aspect of the invention, a method for manufacturinga MEMS resonator includes: forming, on a substrate, a fixed electrodehaving a tapered surface on a side thereof; and forming a movableelectrode above the fixed electrode, having a gap in between, andarranged to face the fixed electrode.

According to the above forth aspect of the invention, the taperedsurface of the side of the fixed electrode makes theside-cross-sectional shape of the fixed electrode smooth, therebypreventing the occurrence of a sidewall-shaped etching residue.Consequently, the status of disturbance in movability of the MEMSstructure or the status of a current leak is improved, thereby providingthe method for manufacturing a highly reliable MEMS resonator.

In this method for manufacturing the MEMS resonator, forming the movableelectrode may further include: forming a sacrifice film on the fixedelectrode; and thereafter forming the movable electrode on the substrateand on the sacrifice film, so that the movable electrode is arranged toface at least part of the fixed electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a schematic top view drawing showing a MEMS resonatoraccording to a first embodiment of the invention.

FIG. 2 is a sectional drawing showing the MEMS resonator according tothe first embodiment of the invention.

FIGS. 3A to 3E are drawings for illustrating a manufacturing method ofthe MEMS resonator according to the first embodiment of the invention.

FIGS. 4A to 4D are drawings for illustrating the manufacturing method ofthe MEMS resonator according to the first embodiment of the invention.

FIG. 5 is a schematic top view drawing showing a MEMS resonatoraccording to a second embodiment of the invention.

FIG. 6 is a sectional drawing showing the MEMS resonator according tothe second embodiment of the invention.

FIGS. 7A to 7D are drawings for illustrating a manufacturing method ofthe MEMS resonator according to the second embodiment of the invention.

FIGS. 8A to 8D are drawings for illustrating the manufacturing method ofthe MEMS resonator according to the second embodiment of the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Embodiments in which the invention is applied will now be described withreferences to the accompanying drawings.

First Embodiment

FIG. 1 is a schematic top view drawing showing a MEMS resonatoraccording to a first embodiment of the invention. FIG. 2 is a sectionaldrawing showing the MEMS resonator according to the first embodiment ofthe invention. The MEMS resonator according to this embodiment includes,as shown in FIG. 2, a substrate 10 and a MEMS structure arranged on thesurface thereof.

A single-crystal semiconductor substrate that is composed of, forinstance, silicon (Si) or gallium arsenide (GaAs) may be used for thesubstrate 10. Particularly, it is desirable that the substrate be thesingle-crystal silicone substrate. A fixed electrode 12 and a movableelectrode 14 composed of polycrystalline silicone are formed on thesurface of the substrate 10.

The fixed electrode 12 has a thin-planar shape as a whole, and isarranged on the substrate 10 via an insulation film 11. On sides of thefixed electrode 12, sidewalls 16 are formed. Here, a sidewall indicatesa state where its thickness increases as it approaches the base of thefixed electrode 12 (the substrate 10). The outer surfaces of thesidewalls 16 may be plane or curve. The sidewalls 16 may have aninclination angle. The inclination angle of the sidewalls 16 is, forinstance, at 5 to 15 degrees inclusive. The fixed electrode 12 is wired,penetrating through a sacrifice film 20 and an insulation film 22, to awiring layer 18 that extends on the insulation film 22. The fixedelectrode 12 is metallized by the wiring layer 18, while it may also bemetallized, using conductors arranged in a different layer than thewiring layer 18, the conductors formed with metals such as Cu, Al, Ta,Cr, and W.

The movable electrode 14 has a thin-planar shape as a whole, and isarranged directly above the fixed electrode 12. The movable electrode 14has a support beam 24, in a structure of so-called cantilever beam. Thesupport beam 24 has a shape of either a band or a bar, and a fixedportion 26 arranged at the end of the support beam 24 is arranged on thesubstrate 10 via the insulation film 11. The movable electrode 14 mayalso be a doubly clamped cantilever beam or a support beam with three ormore clamps. The movable electrode 14 is arranged via a gap 28, facingthe fixed electrode 12. The gap 28 may have a constant distance. Themovable electrode 14 has an inclined surface 40 at the internal surfaceof the support beam 24 of the movable electrode 14 that faces the fixedelectrode 12. The inclined surface 40 may be plane or curve. Theinclined surface 40 may also be a surface that continues to the entireinternal surface of the support beam 24 of the movable electrode 14. Theinclined surface 40 may have an inclination angle. The inclination angleof the inclined surface 40 is, for instance, 5 to 15 degrees inclusive.By providing the inclined surface 40, the support beam 24 may be madelonger. The fixed portion 26 of the fixed electrode 14 is wired,penetrating through the insulation film 22, to a wiring layer 30 thatextends on the insulation film 22. The fixed portion 26 of the fixedelectrode 14 is metallized with the wiring layer 30, while it may alsobe metallized, using conductors arranged in a different layer than thewiring layer 30, the conductors formed with metals such as Cu, Al, Ta,Cr, and W.

An opening 32 is a region that approximately corresponds to a movableportion of the movable electrode 14 and to a part of the fixed electrode12, and is opened so as to ensure the prescribed gap 28 between themovable electrode 14 and the fixed electrode 12.

Here, the movable electrode 14 has a planar shape, and the support beam24 has a shape of a beam (narrow width band or bar), so that when themovable electrode 14 travels in the direction back and forth toward thefixed electrode 12 as described later, mainly the support beam 24 bendsand deforms, and the movable electrode 14 is less likely to deformcompared to the support beam 24. The movable electrode 14 is supportedby the support beam 24, in a state having the gap 28 between the supportbeam 24 and the fixed electrode 12 which is a lower layer on thesubstrate 10. As a result, the movable electrode 14 is in the statewhere it can travel toward the substrate 10 by the elastic deformationof the support beam 24.

A wiring layer insulation film 34 is formed on the wiring layer 18 andon the wiring layer 30, and a protection film 36 is formed on the wiringlayer insulation film 34.

The MEMS resonator according to the first embodiment is driven by eitheran electrostatic attracting force or an electrostatic repulsion forcethat acts on the gap 28 between the movable electrode 14 and the fixedelectrode 12. By impressing a periodically changing voltage between thewiring layer 18 and the wiring layer 30, the electrostatic attractingforce or the electrostatic repulsion force periodically occurs betweenthe fixed electrode 12 and the movable electrode 14, thereby vibratingthe movable electrode 14. In this case, as it is known, the change ofthe periodical voltage between the movable electrode 14 and the fixedelectrode 12 that has direct-current grounding may be generated, byimpressing an alternating voltage to the movable electrode 14.Alternatively, the alternating voltage may be supplied in a state inwhich the DC bias is impressed between the fixed electrode 12 and themovable electrode 14. For instance, a prescribed DC bias voltage is setbetween the fixed electrode 12 and the movable electrode 14, so that aninput signal (alternating voltage) is supplied to the movable electrode14.

In the MEMS resonator according to the first embodiment, when asemiconductor substrate is used as the substrate 10, various kinds ofcircuits such as a drive circuit for driving the above-referencedmovable electrode, an output circuit for obtaining output signals, andan input circuit for introducing input signals are formed in thesemiconductor substrate. That is to say, by forming them on thesemiconductor substrate, the resonator structure and the circuitstructure can be integrated. With such organization of the semiconductordevice, it is possible to make the semiconductor device considerablymore compact, compared to the case of using a separate resonator devicethat corresponds to the above-referenced resonator structure, or thecase where a resonator structure and a circuit structure are constructedas separate bodies. Moreover, wiring redundancy between the circuits canalso be excluded, so that the improvement of characteristics is alsoexpected.

In the MEMS resonator according to the first embodiment, since theinternal surface of the support beam 24 of the movable electrode 14 isthe inclined surface 40, it is possible to make the cross-sectionalshape of the support beam 24 of the movable electrode 14 to be smooth,thereby preventing the occurrence of a sidewall-shaped etching residue,consequently eliminating the negative effect in the vibration movementsof the movable electrode 14. Further, a path of electric leak passbetween the fixed electrode 12 and the movable electrode 14 iseliminated. That is to say, the status of disturbance in movability ofthe MEMS resonator or the status of a current leak is improved.

A method for manufacturing a MEMS resonator according to the firstembodiment of the invention will now be described with references to theaccompanying drawings.

FIGS. 3A to 3E and FIGS. 4A to 4D are drawings for illustrating themanufacturing method of the MEMS resonator according to the firstembodiment of the invention. As shown in FIG. 3A, the substrate 10 isfirst prepared in the manufacturing method of the MEMS resonatoraccording to this embodiment. The substrate 10 is composed with, forinstance, SiN. The thickness of the substrate 10 is, for instance,approximately 100 to 2000 nm by 0.1 nm. Un-illustrated insulation filmcomposed of a material such as silicon oxide (SiO₂) may be formed on thesurface of the substrate 10 by sputtering or by thermo oxidation. Thisinsulation film may also be composed of a native oxide film formednaturally on the surface of the substrate. Moreover, the insulation film11 composed of a material such as silicon nitride (Si₃N₄) may be formedon the insulation film by sputtering or by chemical vapor deposition(CVD). This insulation film 11 is deposited mainly from a manufacturingperspective, and may also function as, for instance, an etch stop filmwhen carrying out the later-described etching of the sacrifice film.

Thereafter, a fixed electrode 12A is formed on the substrate 10 via theinsulation film 11. A method for forming the fixed electrode 12Aincludes, for instance, etching of a MEMS substructure formed on thesubstrate 10. A material used for the MEMS substructure is, forinstance, polycrystalline silicon (poly-Si). The thickness of the MEMSsubstructure is, for instance, approximately 1000 to 4000 nm by 0.1 nm.

Subsequently, as shown in FIG. 3B, an insulation film 38 is formed onthe insulation film 11 and on the fixed electrode 12A. The thickness ofthe insulation film 38 is, for instance, approximately 100 to 4000 nm by0.1 nm. The insulation film 38 is for forming a gap between thelater-described movable electrode 14 and the fixed electrode 12. Theinsulation film 38 is patterned so that it exists, at least, in sideregions of the fixed electrode 12A described later. At this time, it isdesirable that the insulation film 38 is patterned in a way that it islimited to exist only in the side regions of the fixed electrode 12A.

As shown in FIG. 3C, the sidewalls 16 are then formed by etching theinsulation film 38. The sidewalls 16 may also be a surface thatcontinues all around the fixed electrode 12A. In the cross-sectionalshape including the fixed electrode 12A and the sidewalls 16, the bottompart has a wider width than the top part.

As shown in FIG. 3D, the sacrifice film 20 is then formed on the fixedelectrode 12A. By forming the sacrifice film 20, the fixed electrode 12is formed under the sacrifice film 20. A method for forming thesacrifice film 20 includes, for instance, thermo oxidation. Thethickness of the sacrifice film 20 is, for instance, approximately 100to 2000 nm by 0.1 nm. The sacrifice film 20 is for forming a gap, whichwill be described later, between the movable electrode 14 and the fixedelectrode 12. The sacrifice film 20 is patterned so that it exists, atleast, in a region including a forming region of the movable electrode14. At this time, it is desirable that the sacrifice film 20 ispatterned in a way that it is limited to exist only in the formingregion of the movable electrode 14.

As shown in FIG. 3E, the movable electrode 14 is formed on theinsulation film 11, the sacrifice film 20, and on the sidewalls 16, sothat it is arranged facing at least part of the fixed electrode 12. Themovable electrode 14 is formed above the fixed electrode 12 via thesacrifice film 20 and via the sidewalls 16, the movable electrode beingpositioned to face the fixed electrode 12. The movable electrode 14 hasa support beam 24, in a structure of so-called cantilever beam. Thesupport beam 24 has a shape of either a band or a bar, and the fixedportion 26 arranged at the end of the support beam 24 is arranged on thesubstrate 10 via the insulation film 11. A method for forming themovable electrode 14 includes, for instance, etching of a MEMSsuperstructure formed on the substrate 11 and on the sacrifice film 20.A material used for the MEMS superstructure is, for instance, poly-Si.The thickness of the MEMS superstructure is, for instance, approximately1000 to 4000 nm by 0.1 nm.

Subsequently, as shown in FIG. 4A, the insulation film 22 is formed onthe insulation film 11, the sacrifice film 20, the fixed electrode 12,and on the sidewalls 16. Materials used for the insulation film 22 are,for instance, tetra-ethyl-ortho-silicate (TEOS) and borophosphosilicateglass (BPSG, or, silicate glass film). The thickness of the insulationfilm 22 is, for instance, approximately 1000 by 0.1 nm for TEOS, andapproximately 8000 by 0.1 nm for BPSG.

As shown in FIG. 4B, the wiring layers 18 and 30 are formed on theinsulation film 22. The wiring layer 18 penetrates through the sacrificefilm 20 and the insulation film 22, extends on the insulation film 22,and is connected to the fixed electrode 12. The wiring layer 30penetrates through the insulation film 22, extends thereon, and isconnected to the fixed portion 26 of the fixed electrode 14. A materialused for the wiring layers 18 and 30 is AlSiCu or AlCu (alloy thatincludes aluminum). The thickness of the wiring layers 18 and 30 is, forinstance, approximately 5000 to 20000 nm by 0.1 nm. All the structuralelements that constitute the MEMS resonator are formed on the substrate10 after the completion of this process.

As shown in FIG. 4C, the wiring layer insulation film 34 is then formedon the insulation film 22 and on the wiring layers 18 and 30. The wiringlayer insulation film 34 is formed, for instance, with CVD method. Thethickness of the wiring layer insulation film 34 is, for instance,approximately 5000 to 10000 nm by 0.1 nm.

Further, the protection film 36 is formed on the wiring layer insulationfilm 34. The protection film 36 is formed, for instance, with CVDmethod, so as to form an oxide film and a nitride film. The thickness ofthe protection film 36 is, for instance, approximately 4000 by 0.1 nmfor the oxide film, and approximately 4000 to 10000 by 0.1 nm for thenitride film.

Thereafter, as shown in FIG. 4D, a MEMS release window is opened. TheMEMS unit release window opens from the top of the protection film 36down to the top of the movable electrode 14, forming an opening 32A,approximately corresponding to a movable portion of the movableelectrode 14.

Subsequently, as shown in FIG. 2, the MEMS unit is released. Byreleasing the MEMS unit, a part of the sacrifice film 20 and of thesidewalls 16 corresponding to the opening 32A is removed, therebyforming the opening 32 so that the prescribed gap 28 is secured betweenthe movable electrode 14 and the fixed electrode 12. In releasing theMEMS unit, part of the sacrifice film 20 and of the sidewalls 16 thatcorresponds to the opening 32A is removed by carrying out a wet etchingusing an etching fluid of hydrofluoric acids. By eliminating thegeneration of the foreign particles during the release etching, atime-wise processing margin of the release etching increases.

With the manufacturing method of the MEMS resonator according to thefirst embodiment, the internal surface of the support beam 24 of themovable electrode 14 is made to be the inclined surface 40 by formingthe sidewalls 16 on the sides of the fixed electrode 12; hence, it ispossible to make the cross-sectional shape of the support beam 24 of themovable electrode 14 smooth. Consequently, an occurrence of thesidewall-shaped etching residue of the movable electrode 14 isprevented, eliminating the generation of foreign particles during therelease etching. By eliminating the generation of the foreign particlesduring the release etching, a margin of a time-wise processing in therelease etching increases, as does the margin of a process-wisemanufacturing condition (i.e., etching of the movable electrode 14).

Second Embodiment

FIG. 5 is a schematic top view drawing showing a MEMS resonatoraccording to a second embodiment of the invention. FIG. 6 is a sectionaldrawing showing the MEMS resonator according to the second embodiment ofthe invention. The MEMS resonator according to the second embodiment ofthe invention includes, as shown in FIG. 6, the substrate 10 and theMEMS structure arranged on the surface thereof.

The fixed electrode 12 includes tapered surfaces 42 at its sides. Here,“taper” indicates a state where the thickness of the fixed electrode 12decreases toward its edge. The tapered surfaces 42 may be plane orcurve. The tapered surfaces 42 may also be a surface that continues allaround the fixed electrode 12. The tapered surfaces 42 may have aninclination angle. The inclination angle of the tapered surfaces 42 is,for instance, 5 to 15 degrees inclusive. The cross-sectional shape ofthe tapered fixed electrode 12 is wider at the bottom than at the top.

In the MEMS resonator according to the second embodiment, the occurrenceof sidewall-shaped etching residues of the movable electrode 14 isprevented, since the cross-sectional shape of the sides of the fixedelectrode 12 is made smooth with the tapered surfaces 42 at the sides ofthe fixed electrode 12, thereby eliminating the negative effect in thevibration movements of the movable electrode 14. The area in which thefixed electrode 12 faces the movable electrode 14 increases, since thetapered surfaces 42 at the sides of the fixed electrode 12 also face themovable electrode 14. Consequently, the electrostatic attracting forceand the electrostatic repulsion force acting between the fixed electrode12 and the movable electrode 14 increase.

A method for manufacturing the MEMS resonator according to the secondembodiment of the invention will now be described with references to theaccompanying drawings.

FIGS. 7A to 7D and FIGS. 8A to 8D are drawings for illustrating themanufacturing method of the MEMS resonator according to the secondembodiment of the invention. As shown in FIG. 7A, the substrate 10 isfirst prepared in the manufacturing method of the MEMS resonatoraccording to this embodiment.

Thereafter, the fixed electrode 12A that has tapered surfaces 42A at itssides is formed on the substrate 10 via the insulation film 11. At thistime, dopants are introduced to the MEMS substructure and an etchingcondition is configured such that the side surfaces are obliquelytapered.

As shown in FIG. 7B, the sacrifice film 20 is then formed on the fixedelectrode 12A.

As shown in FIG. 7C, the movable electrode 14 is then formed on theinsulation film 11 and on the sacrifice film 20, so that it is arrangedfacing at least part of the fixed electrode 12. The movable electrode 14is formed above the fixed electrode 12 via the sacrifice film 20, themovable electrode 14 being positioned to face the fixed electrode 12.

As shown in FIG. 7D, the insulation film 22 is then formed on theinsulation film 11, the sacrifice film 20, and on the fixed electrode12, in a way that the top surface of the insulation film 22 isflattened.

Thereafter, as shown in FIG. 8A, the wiring layers 18 and 30 are formedon the insulation film 22. All the structural elements that constitutethe MEMS resonator are formed on the substrate 10 after the completionof this process.

As shown in FIG. 8B, the wiring layer insulation film 34 is then formedon the insulation film 22 and on the wiring layers 18 and 30.

Thereafter, as shown in FIG. 8C, the protection film 36 is formed on thewiring layer insulation film 34.

Subsequently, as shown in FIG. 8D, the MEMS release window is opened.The MEMS release window opens from the top of the protection film 36down to the top of the movable electrode 14, forming an opening 32A,approximately corresponding to a movable portion of the movableelectrode 14.

As shown in FIG. 6, the MEMS unit is then released. By releasing theMEMS unit, the sacrifice film 20 in the portion corresponding to theopening 32A is removed; thereby forming the opening 32 so that theprescribed gap 28 is secured between the movable electrode 14 and thefixed electrode 12. In releasing the MEMS unit, by carrying out a wetetching using an etching fluid of hydrofluoric acids, part of thesacrifice film 20 that corresponds to the opening 32A is removed.

In the method for manufacturing the MEMS resonator according to thesecond embodiment, the occurrence of sidewall-shaped etching residues ofthe movable electrode 14 is prevented, since the side cross-sectionalshape of the fixed electrode 12 is made smooth with the tapered surfaces42, thereby eliminating the generation of the foreign particles duringthe release etching. As for the rest of the composition and themanufacturing methods, what has been described in the first embodimentmay be applied.

The present invention shall not be limited to the embodiments mentionedabove, and may be applied to the any structure forming in a MEMS-CMOSintegration process. For instance, other MEMSs include devices such asswitches, resonators, acceleration sensors, and actuators.

The entire disclosure of Japanese Patent Application Nos: 2005-332444,filed Nov. 17, 2005 and 2006-261135, filed Sep. 26, 2006 and2005-332445, filed Nov. 17, 2005 are expressly incorporated by referenceherein.

1. A MEMS resonator, comprising: a substrate; a fixed electrode formedon the substrate; and a movable electrode arranged facing the fixedelectrode; wherein the fixed electrode has a tapered surface on a sidesurface portion facing the movable electrode, and wherein an internalsurface of a support beam of the movable electrode facing the taperedsurface of the fixed electrode has an inclined surface.
 2. The MEMSresonator as set forth in claim 1, wherein the tapered surface of thefixed electrode has an inclination angle.
 3. The MEMS resonator as setforth in claim 2, wherein the inclined surface of the support beam hasan inclination angle.
 4. The MEMS resonator as set forth in claim 1,wherein a gap between the tapered surface of the fixed electrode and theinclined surface of the support beam of the movable electrode isconstant.
 5. The MEMS resonator as set forth in claim 1, wherein themoveable electrode comprises a movable portion, and wherein the moveableportion is a portion extending from the support beam of the movableelectrode.
 6. A method for manufacturing a MEMS resonator, comprising:forming, on a substrate, a fixed electrode having a tapered surface on aside surface portion; forming a sacrificial film on an upper surfaceportion of the fixed electrode and on the tapered surface of the fixedelectrode; forming, on the substrate and on the sacrificial film, amovable electrode and a support beam of the movable electrode, so thatat least part of the upper surface portion of the fixed electrode andthe tapered surface of the fixed electrode are arranged opposite to eachother; and removing the sacrificial film.